EXPLANATION OF PLATES XIII, TLN—Con(mted. 



Fig. 5 shows, in addition, the olfactory pit and the distal end of the 

 olfactory nerve. 



Fig. 6 shows the third, glossopharyngeal and vagus nerves. 



Figs. 7 and S. — Longitudinal and vertical sections through the cerebral 

 hemispheres and nasal region of a six-day chiek embryo. Picric acid. 

 X 15 diam. 



Fig. 7 shows whole length of olfactory nerve. 



Fig. 8 shows ganglion at root of origin of olfactory nerve, also internal 

 projection of hemisphere at this point. 



Fig. 9. — Longitudinal and vertical section through the nasal region of a 

 seven-day chick embryo, showing whole length of olfactory nerve, and com- 

 mencing rudiment of olfactory lobe. Picric acid, x 15 diam. 



Fig. 10. — About half of a transverse section through the forebrain of a 

 four-day duck embryo, showing the olfactory nerve and pit. Picric acid. 

 X 50 diam. 



Figs. 11 and 12. — Tranverse sections through the anterior part of the 

 head of an eighty-hours' chick embryo, passing through the cerebral hemi- 

 spheres, and the olfactory pits and nerves. Picric acid, x 27 diam. 



Fig. 11 shows on left side the origin of the olfactory nerve. 



Fig. 12 shows on right side the distal end of the olfactory nerve. 



Fig. 13. — Longitudinal and horizontal section through the head of a 

 dogfish embryo of stage k, showing early stage in development of the 

 olfactory pits. Chromic and osmic acids, x 20 diam. 



Fig. 14. — Transverse section through the anterior extremity of the head 

 of a dogfish embryo of stage k, showing the forebrain, the olfactory pits and 

 nerves. Chromic and osmic acids. X 20 diam. 



Fig. 15. — Longitudinal and vertical section through the head of a dogfish 

 embi-yo of stage m, showing the olfactory pit and nerve. Chromic and 

 osmic acids, x 20 diam. 



Fig. 16. — Longitudinal and vertical section through the head of a dogfish 

 embryo of stage M, showing the olfactory pit, the mandibular, hyoid and 

 branchial arches. Chromic and osmic acids, x 20 diam. 



Figs. 17 and IS. — Longitudinal and vertical sections through the head 

 of a dogfish embryo of stage o. Chromic and osmic acids, x 20 diam. 



Fig. 17 shows olfactory pit and nerve. 



Fig. IS shows olfactory pit, with Schneiderian fold, olfactory nerve, fore- 

 brain, hyoid and branchial arches. 



Fig. 19. — Transverse section through the forebrain of a dogfish embryo 

 of stage M, showing olfactory pits and nerves, with absence of olfactory 

 lobes. Chromic and osmic acids, x 27 diam. 



Fig. 20. — Transverse section through the same region as in the preceding 

 figure, but in a dogfish embryo at the commencement of stage o : shows 

 olfactory pits with Schneiderian folds, olfactory nerve, and commencing 

 olfactory lobe. Chromic and osmic acids, x 27 diam. 



Fig. 21. — Transverse section through the forepart of the head of a dogfish 

 embryo at a stage intermediate between o and r, showing the forebrain, 

 the olfactory pits, and on the left side the olfactory nerve and olfactory 

 lobe. X 17 diam. 



Fig. 22. — Transverse section through the forepart of the head of a dog- 

 fish embryo of stage Q, showing the cerebral hemispheres, olfactory lobes, 

 olfactory nerves, and olfactory pits with their Schneiderian folds, x 9 

 diam. 



Figs. 23 — 26. — Sections through a dogfish embryo of stage n, showing 

 the resemblances between the gills and the Schneiderian folds. Chromic 

 and osmic acids. 



